6th International Symposium on Soil Organic Matter

Meeting report by Tom SizmurUniversity of Readingt.sizmur@reading.ac.ukECG Bulletin February 2018

More than 400 delegates from 44 different nations descended upon Rothamsted Research in Hertfordshire, UK, during four days in September 2017 for the 6th International Symposium on Soil Organic Matter, which saw more than 180 talks and 230 poster presentations.

The conference opened with a welcome from Rothamsted Research Director Professor Achim Doberman, who introduced some of the long term experimental findings that make Rothamsted a world famous institute for the study of soil organic matter. Back when the Broadbalk experiment (now the longest continuously running agricultural experiment in the world) was started in 1843, the intention was to compare the standard practice of applying organic manure with the relatively new concept of mineral fertilisers. It is therefore rather ironic that there is greater interest today in the elevated soil organic matter, and its associated benefits, found in the manured plots than in that from plots treated with mineral fertilisers, which is now standard practice.

Several themes emerged throughout the conference: perhaps the strongest of these was the need to develop the next generation of soil organic matter decomposition models and for experimental scientists to work more closely with modellers (and vice versa). This was first raised in a keynote address by Professor Michael Schmidt, whose 2011 paper in Nature [1] revolutionised the field by suggesting that ‘stable’ soil organic matter was not plant matter that had resisted decay over time due to its chemical composition, but in fact largely consists of microbial products that, despite being thermodynamically unstable, are physically and chemically protected from decomposition by soil aggregates and physical sorption on soil surfaces.

The challenge of generating the data to represent these processes in soil organic matter decomposition models was taken up by several presenters using stable isotopes to track the movement of carbon through soils, and was introduced in keynote presentations from Professors Francesca Cotrufo and Richard Evershed. Another experimental technique that dominated many talks was the use of physical fractionation methods. These methods use sieving and density separation to isolate fractions of the soil organic matter occluded within aggregates from fractions that are chemically adsorbed to soil surfaces. An interlaboratory comparison of several such protocols was presented by Dr Christopher Poeplau.

Towards the end of the conference, Professor Henry Janzen gave an inspiring talk on the topic of soil health, providing a much-needed definition of soil health as being the combination of soil functions, vitality, and time. In agreement with most soil scientists, he identified soil organic matter as the preeminent indicator of soil health. Professor Janzen asserted that a key facet of soil organic matter was as a dynamic repository of solar energy and that this solar energy, when respired by soil organisms, provides many of the ecosystem functions that are associated with healthy soils.

The conference ended with a closing ceremony in which Professor David Powlson gave a dedication to the late Professor David Jenkinson, who pioneered many of the techniques presented in the conference, including the creation of soil organic matter models, the measurement of the soil microbial biomass, and the use of stable and radioactive isotopes to study C and N cycling in soils. Powlson closed his talk with this advice to early career scientists: “Listen to advice from experienced scientists. Consider the advice – sometimes act on it. But don’t be constrained by it – be bold and develop fresh ideas!”